Aneurysm Rupture after Endovascular Flow Diversion: The Possible Role of Persistent Flows through the Transition Zone Associated with Device Deformation

Abstract

<jats:p> Haemorrhagic complications can occur following aneurysm treatment with flow diverters (FD), but the underlying mechanism remains unknown. We describe a case where deformation of the device may have contributed to the complication. </jats:p><jats:p> A patient with a giant, previously unruptured cavernous aneurysm that extended intracranially to cause oedema of the internal capsule was treated with flow diversion. Treatment was followed by multiple episodes of peri-aneurysmal haemorrhages within eight days. A deformation of the device which occurred where it curved to cross the aneurysm neck created residual flows which, in the presence of a stent stenosis immediately beyond the neck, may have contributed to the observed ruptures. Following multiple haemorrhages the patient subsequently died. </jats:p><jats:p> Autopsy demonstrated early red thrombus partially bridging the struts of the flow diverter, and intra-aneurysmal thrombus of various ages. Microscopic pathology showed an aneurysm wall consisting of collagen infiltrated with neutrophils, but the wall was absent near the cerebral peduncle, adjacent to the brain haemorrhage. </jats:p><jats:p> Radiographs of the extracted specimen confirmed deformation of the FD construct, located at the transition zone of the stent, leading to increased pore size and porosity. The site of the deformation correlated with the angiographic presence of a continued blood inflow jet into the aneurysm. </jats:p><jats:p> Stent deformation at the transition zone may promote persistent blood entry into the aneurysm, and in turn potentially contribute to haemorrhagic complications. </jats:p>

International Retrospective Study of the Pipeline Embolization Device: A Multicenter Aneurysm Treatment Study

“…1,3,8,9 Severe and unexpected adverse events include spontaneous rupture of treated aneurysms and intraparenchymal intracranial hemorrhage unrelated to aneurysm rupture. 8,[10][11][12] These reports led to policies in some regions mandating concomitant coil embolization with flow-diverter therapy to mitigate the risk of spontaneous aneurysm rupture. 13 Most previous literature on flow-diversion therapy comprised single-center case series, either retrospective or prospective, and has substantial selection bias, which may affect the rates of severe and unexpected adverse events.…”

Tapered flow diverters in the treatment of intracranial aneurysms

“…Focal zones of low porosity and residual flow specifically occur in curved segments or wide-neck aneurysms due to the deformation of the FD (8,13). This deformation at the TZ is a potential cause of failure of flow diversion in wide-neck curved and/or endwall aneurysms (2,(6)(7)(8)13). …”

“…In other words, as there is a direct relation between lower porosity of the 'free segment of the stent' (FSS) facing the aneurysm cavity and success of aneurysm occlusion (6,7), the increased porosity at TZ will result in sustained leak into the aneurysm and increase the risk of residual aneurysms after flow diversion (2,9,13,15,16). Focal zones of low porosity and residual flow specifically occur in curved segments or wide-neck aneurysms due to the deformation of the FD (8,13). This deformation at the TZ is a potential cause of failure of flow diversion in wide-neck curved and/or endwall aneurysms (2,(6)(7)(8)13).…”

Y-Crossing of Braided Stents with Stents and Flow Diverters Does Not Cause Significant Stenosis in Bench-Top Studies

“…We studied the lvIS device as the first braided stent, and a selection of second crossing braided devices; results may not apply to all braided stents and FDs. Bench-top experiments were done in artificial conditions, and while some of the described deformations have been documented in experimental animals 18 and some clinical cases [27][28] , it is unclear how often…”